Unified air control for burners



July 17, 1956 E. D. PHILLIPS 2,754,845

UNIFIED AIR CONTROL FOR BURNERS Filed March 18, 1952 2 Sheets-Sheet l INVENTOR EVERETT D. PHILLIPS Mws ATTORNEY July 17, 1956 v E. D. PHILLIPS 2,754,845

UNIFIED AIR CONTROL FOR BURNERS Filed March 18. 1952 ZSheets-Sheet 2 FIG. 52 5| 8O FURNACE BURNER 3 G BLOWER AIRCONTROL M 1g: MOTOR I LPULVERIZER v FIG. 8 84 7 W A V INVENTOR b i J EVERETT D. PHILLIPS 2o \il 20 BY 56 55 4 7\TToRNEY United States Patent UNIFIED AIR CONTROL FOR BURNERS Everett 1). Phillips, Danville, Pa.; Rubye W. Phillips, executrix of said Everett D. Phillips, deceased Application March 18, 1952, Serial No. 277,178 2. Claims. (Cl. 137-608) This invention relates to furnace firing equipment and more particularly to a unified draft control for regulating each of the various air streams required by a burner;

Although my invention may be used with appreciable benefits in the supplying of air to gas and liquid fired burners, it is primarily designed for use with burners utilizing pulverized, solid fuels. The use of pulverized, solid fuels has been steadily declining because of the complications attendant the existing equipment in making both the initial and operating adjustments. In the conventional, pulverized, solid fuel burner the air is introduced to the burner by means of three separate streams conventionally designated as the primary air, secondary air and tertiary air. The quantative proportioning of these air streams is most important, if optimum combustion conditions are to be maintained. Proportioning of these airs must be adapted to the burning characteristics of the particular fuel involved. At the same time, this proportioning partially determines the shape of the flame. In turn, the shape of the flame has much to do with the overall efficiency of the furnace.

Conventional, pulverized, solid fuel burners require a minimum of two and often three or more sets of dampers each of which must be simultaneously regulated and their operation synchronized. Whenever it is necessary to vary the thermal output of the burner it is necessary to adjust each of these dampers and thereafter again synchronize their operation to properly proportion the volume of these air streams. This results in appreciable lack of efficiency and excessive loss of time. During the adjustment period the burner will not operate efficiently. The period of adjustment required after each change may take hours or even days to complete. Because, at best, this arrangement of a number of different, individual dampers, each regulated independently of the other, the average burner may operate only within the range of- 50% to 100% of its capacity.

The conventional arrangement of dampers for pulverized, solid fuel burners creates a serious ditficulty when the burner is first started because it is difiicult to obtain a proper mixture to sustain combustion. If combustion is not sustained, the furnace must be purged of any pulverized fuel before reignition is attempted. Failure to do this may result in an explosion. Under such conditions the starting of a furnace requires a highly skilled operator and sometimes may occupy his time for many hours.

It is therefore a primary object of my invention to simplify and reduce to a minimum the number of operations necessary for successfully firing and thereafter operating a pulverized, solid fuel burner.

It is a further object of my invention to eliminate all unnecessary and surplus equipment, substitute therefor a single, compact, efiicient, automatically synchronized control.

An additional object of my invention is to extend the their full capacity, preferably as low as 10% of their capacity.

A further additional object of my invention is to reduce both the capital investment and the operational costs involved in operating and maintaining a furnace fired by pulverized, solid fuels.

These and other objects and purposes of my invention will be immediately seen by those acquainted with boiler designs and furnace burner equipment upon reading the following specification and the accompanying drawings.

In the drawings:

Figure 1 is a side, elevation view of my invention with a small portion of the side wall broken out.

Figure 2 is a plan view of my invention with a portion of the cover removed to expose the internal operating structure.

Figure 3 is a sectional, elevational view taken along the plane III-III of Figure 1.

Figure 4 is a fragmentary view of a typical mounting for one of the auxiliary dampers.

Figure 5 is a fragmentary, enlarged view of a portion of the auxiliary damper control mechanism.

Figure 6 is a typical view of an auxiliary damper equipped with a filler plate.

Figure 7 is a sectional, elevation plane VII-VII of Figure 6.

Figure 8 is a diagrammatic presentation of a complete furnace firing installation incorporating my invention.

In executing the objects and purposes of my invention, I have provided an air stream distributing and draft control chamber consisting of a box of any desired geometrical shape to which-a firing fluid such as air is supplied by a single source. The air is introduced to a plenum chamber from which it passes into a plurality of smaller chambers through orifices which may be changed both in width and shape. The air is removed from the box by means of a plurality of exhaust ports one connected to each of the smaller chambers. A main damper is provided, operating simultaneously upon each of the orifices for controlling the total quantity of air delivered to the burner. The controls are so designed that the proportion of air sent to the burner in each air stream may be individually established and after this proportion has been once determined the'overall volume of air may be regulated without disturbing this proportion.

In the following description the terms upper and lower are frequently used and are to be taken to mean upper toward the top of the box as it appears in Figure 1 and lower away therefrom. It will be recognized that this particular orientation of the box is utilized only to view taken along the simplify the description thereof and is not to be conmay be operated at loads substantially less than one-half sidered as a limitation as to the particular way in which the box will be arranged at the time of installation.

Referring now to the drawings in detail, the numeral 1 indicates a draft control having a rectangular housing 2 enclosing an upper plenum chamber 3 and three lower chambers, a primary air chamber 4, a secondary air chamber 5, and a tertiary air chamber 6. The three lower chambers 4, 5 and 6 are separated from the plenum chamber 3 by a plate 7 and from each other by baflies 18. At one end, three rectangular apertures are provided through the plate 7. The aperture 8 provides communication between the plenum chamber 3 and the primary air chamber 4, the aperture 9 between the plenum chamber 3 and the secondary air chamber 5 and the aperture 16 between the plenum chamber 3 and the tertiary air chamber 6. These apertures are aligned across the plate 7 with their greater dimension arranged longitudinally of the housing. The purpose of this arrangement will be explained more fully hereinafter.

Mounted on top of the plate 7 for sliding movement longitudinally of the housing is a main damper 11. The main damper 11 consists of a plate having a rack 12 along each side. The main damper is of such length that it may be caused to cover entirely the apertures 8, 9 and 10, without disengaging the hereinafter described pinions 14. The housing 2 is of such length that the main damper may be withdrawn to entirely expose the apertures 8, 9 and 10. The main damper 11 is guided by a rail strip 13 along each side. The rail strips 13 are attached to the plate 7 by suitable means such as screws or welding.

Movement of the main damper 11 is effected by rotation of the pinions 14 engaging the racks 12. The pinions 14 are each mounted on the shaft 15 journaled at each side of the housing 2 in the bearings 16. On one end the shaft 15 is equipped with a hand wheel 17. The showing of the hand wheel 17 is illustrative only. It will be recognized that any suitable power means, with or without automatic controls, may be substituted for the hand wheel. In addition, any other mechanical means for sliding the main damper 11 such as a pneumatic or hydraulic cylinder may be substituted for the racks and pinions.

Each of the apertures 8, 9 and 10 is provided with a separate, independently operable damper. For this an L-shaped track 20 is mounted along each of two sides of each of the apertures. These tracks 20 are secured to the lower surface of the plate 7 and are arranged transversely of the housing 2 adjacent the short sides of the apertures. Each of these tracks supports an auxiliary damper plate between it and the plate 7. Each of the auxiliary dampers is of such size that it may entirely close its related aperture. The auxiliary damper 21 for the primary air has, at its center, a depending lug 22, centrally threaded to receive the externally threaded tube 23. The tube 23 has one end within the primary air chamber 4 and the other end extending through the side of the housing 2 to mount the handle 24. Between the handle 24 and the housing 2 is a friction reducing element 25.

Extending through the tube 23 is an inner tube 26. The inner tube 26 projects outwardly beyond the handle 24 to mount a second handle 27. The second handle 27 is separated from the first handle by a friction reducing element 28. The inner end of the inner tube extends into the secondary air chamber where it is externally threaded to engage the lug 29 mounted to the center of the auxiliary damper 30 for the aperture 9.

Extending through the inner tube 26 is a rod 31. At one end, the rod 31 projects beyond the inner tube to mount a third handle 32 separated from the second handle by a friction reducing element 33. At the other end, the rod 31 extends through the tertiary air chamber 6 and, externally of the housing 2, is secured by a collar 34. Within the tertiary air chamber 6, the rod 31 is threaded to engage the lug 35, mounted to the center of the auxiliary damper 36 for the aperture 10.

The rod 31 and the tubes 23 and 26 may each be independently rotated without eflecting movement of the others. Both the tubes and the rods are held against axial movement in either direction whereby, upon rotation, each will move the auxiliary damper to which it is engaged.

Air is introduced to the plenum chamber 3 through the port 50, which is of such size that it may supply the combined, maximum air demand of the primary, secondary and tertiary air chambers. The primary air chamber 4 is vented through the port 51, the secondary air chamber is vented through the port 52 and the tertiary air is vented through the port 53.

In many installations it is necessary to change the shape of the apertures 8, 9 and to something other than a rectangle. For this purpose filler plates are provided. A typical filler plate is shown in Figures 6 and 7. The filler plate 40 consists of a strip slightly rounded on each end and designed to be mounted to the upper surface of an auxiliary damper, such as the auxiliary damper 36. The filler plate 40 is of the same or lesser width, as required, than the aperture over which the auxiliary damper is movable and has a thickness preferably the same as but no greater than that of the plate 7. The filler plate 40 is attached to the auxiliary with its leading edge 41 coinciding with the leading edge of the auxiliary damper projecting into the aperture. Attachment is effected by a screw 42 mounted at the center of the filler plate 7. Approximately midway between each end of the filler plate 40 and the screw 42 is a slot 43 opening through the trailing edge 44 of the filler plate. The slots 43 are inclined to the trailing edge 44 whereby the plate may be pivoted about the screw 42 without binding with the screw 45 in each of the slots 43. The screws 4-5 are secured to the auxiliary damper 36. As will be explained more fully hereinafter, the filler plate 40, normally, need only pivot in one direction. Therefore, the screws 45 are not the same distance from the trailing edge 44 of the plate but are arranged to permit this pivotal movement without disengagement from the slot or binding with the end of the slot. The screw 42 and the screws 45 are each countersunk to provide a flush upper surface which will not interfere with the main damper 11. It will be recognized that where greater flexibility of adjustment of the filler plates 40 is desired, the slots 43 may be lengthened to permit pivotal movement in two directions rather than limited to a single direction as described.

While I have described my filler plate 40 as mounted upon the auxiliary damper 36, this is for simplification only. An identical filler plate 40 may or may not be similarly mounted on each of the other auxiliary dampers 21 and 30. Whether additional filler plates are used will depend upon the operating conditions and type of burner with which my draft control is used.

The housing 2 and the various other parts of my draft control mechanism may be fabricated from any suitable material, preferably steel sheet or plate. Where rigid joints are desired, welding is a preferable joining means because it is permanent and provides an effective seal against air leaks. This latter is important because the draft control is designed to be used with air supplied to it from a blower. It is important that the various parts of my invention be carefully made to close tolerances to prevent air leaks about the various dampers. Such leaks have been found to cause serious difficulties in properly regulating the burner. Where necessary, a heavy grade of felt may be used between relatively movable parts to seal joints which otherwise would permit air leakage. Felt is satisfactory for this purpose because adjustment of the dampers is done gradually and infrequently.

Operation My invention is designed to provide a unified control for the total air supply for a furnace burner. My invention may be used with an induction system or with a pressure system. The choice of system with which it is utilized depends upon the type of burner and the type of pulverizer employed if the draft control is utilized with a solid fuel burner. Although the burner may be used with an induction system, it is primarily designed for and is most advantageous when operated with a pressurized system whereby the blower is placed ahead of the draft control and the air is under pressure when it enters the draft control.

In the following description it is assumed that the draft control is used with a pressurized system in which case all of the air to be used by the burner is introduced to the plenum chamber 3 through the port 50. This air is then divided into three air streams representing the primary air, secondary air and tertiary air for the burner. This division of the total air into three streams is effected by means of the three apertures 8, 9 and 10. These ports operate to actually measure the volume of air passing through them.

In the case of every burner, the relative quantum of air demanded in each stream by the burner is different. Further, the relative proportions of the air volume of each stream may vary from time to time due to fluctuations in the type and condition of the fuel utilized. Thus, it is necessary to provide a separate means for independently regulating the volume of each of these air streams. Under normal operating conditions approximately to 25% of the total combustion air is provided by means of the primary air stream. The remainder of the combustion air is provided by means of the secondary air stream. Thus, the secondary air stream normally must carry three or more times the volume of air as that of the primary air stream. When wet fuel is used or a solid fuel pulverizer is employed which absorbs abnormal quantities of the kinetic energy of the primary air stream, it becomes necessary to supplement the primary air stream at the pulverizer or at the burner with a small quantity of tertiary air. Normally, the volume of tertiary air will be substantially smaller than the volume of either the primary or secondary air streams. it is for this purpose that my draft control provides an individual damper for each air stream. By rotation of the handle 32, the auxiliary damper 36 may be opened or closed independently of the other dampers to establish the desired proportion of tertiary air admitted to the burner with relation to the primary and secondary airs. At the same time by manipulation of the handle 27 the auxiliary damper 30 may be caused to open or close the secondary air aperture 9 whereby the volume of secondary air may be independently regulated to properly proportion it to both the tertiary and primary airs. Manipulation of the handle 24 will effect independent regulation of the primary air. Thus, by independent adjustment of eachof the auxiliary dampers a proportioning of the total volume of air demanded by the burner for complete combustion may be effected to produce an ideal combustion mixture. Since each of the auxiliary dampers 21, 3t) and 36 is moved by a positive mechanism, each of these dampers may be precisely adjusted to obtain an exact proportioning to meet the demands of the burner. Generally, when these dampers are once set they will not again be adjusted. However, these proportions may be quickly and easily changed at any time to meet changing conditions at the burner.

For proper regulation of the burner it is not only necessary to correctly proportion the volume of each of the primary, secondary and tertiary air streams, but it is also necessary, from time to time, to vary the total quantity of air being introduced to the burner. This regulation is necessary to vary the capacity at which the burner is operated. When only a small amount of steam is demanded by the plant, the burner should be operated with a reduced flame in order to economize fuel. To reduce the flame it is necessary to reduce the total quantity of air being introduced to the burner. This has been accomplished by individually regulating the dampers of each of the separate air streams. Such a procedure normally results in a disturbance in the proper proportions between the separate air streams. Because of this, the operation required a resetting of these proportions each time it is necessary to regulate the total thermal output of the burner. When done manually, the operation often entailed one or more hours of careful adjustment each time it was necessary to vary the thermal output of the burner. It is precisely this difliculty which is eliminated by my invention. By rotating the handle 17, the main damper 11 is caused to open or close each of the three apertures 8, 9 and 10 simultaneously, substantially instantaneously without disturbing the established proportions of the air streams. The total volume of air passing to the burner may be quickly and easily regulated without in any way disturbing the established proportional relationships between the separate air streams. Thus, regulation of the thermal output of the burner is reduced from a time consuming, laborious adjustment to a simple operation involving but a few moments of an operators time to complete.

This permits the burner to be operated at a much smaller percentage of its full capacity than was heretofore possible. As the operation of the burner is reduced below 50% of capacity the correct proportioning of the various air streams and of the fuel to air becomes increasingly critical in maintaining a flame. Where, heretofore, this proportioning had to be re-established with each change in operating level, it was substantially impossible to maintain ignition. With my invention, however, the operating level may be changed without variation of these critical factors. Therefore, the operating level of the burner may be safely reduced far below that previously possible. This will result in appreciable fuel savings during periods of partial operation or short nonoperating periods such as Week-ends.

As the total quantity of air supplied to the burner is varied by means of the main damper 11, it often happens that the proportions between the various air streams must be changed. The amount of variation and which air streams will be affected are dependent upon many conditions. Among the factors having a bearing upon this is the type of pulverizing equipment employed. Pulverizers effecting fine grinding require different settings from those effecting coarse grinding. This is also true of constant speed pulverizers as compared with variable speed ones. The condition of the fuel itself will have an important bearing, wet fuel requiring a greater air volume than dry fuel to effect transportation. As an example, when the total volume of air supplied to the burner is reduced substantially, with certain equipment it happens that the volume of air passing through the pulverizer is insufiicient to carry the required quantity of fuel to the burner. It thus becomes necessary to vary the proportions between the various air streams whereby a greater quantity of the total air volume is directed through the primary air stream and the volume of the secondary and tertiary air streams reduced by an equal amount. This is the function of the filler plates 40. This amount of variation in the proportions can be initially established. :Once established, the filler plates 40 may be set to effect the desired change and thereafter need not again be rearranged. This is but one example of the numerous variables which may be compensated by the filler plates 40.

The change in relative proportions between the air streams as the main damper 11 is moved may be effected by setting the filler plates at an angle to the leading edge of the auxiliary dampers whereby the resulting apertures are no longer rectangular. Thus, where it is desired to change the relative proportions between the primary and secondary air streams as the main damper 11 is closed to reduce the operating level of the burner, the filler plate 40 on the auxiliary damper 21 is inclined to form a tapered opening with the end of greatest width away from the main damper 11. At the same time, the filler plate 40 on the auxiliary damper 30 is inclined the same amount but in the opposite direction whereby the end of greatest width of the opening is adjacent the main damper 11. Thus, as the damper 11 is closed, the size reduction of the aperture 8 through which the primary air is measured is slower than the size reduction of the other two apertures. At the same time, the closure of the secondary air aperture 9 is gradually accelerated. This has the efiect of gradually transferring at a predetermined rate, the necessary quantity of air from the secondary air stream to the primary air stream without disturbing the air to fuel ratio at the burner. As the main damper 11 is opened this procedure is reversed and the original proportions automatically established.

The integration of my unified air control in a complete furnace firing system is more completely shown in Figure 8 wherein the blower introduces to the system the entire air to be used by the burner. By means of. the blower 80 the air is forced into the air control mechanism 1 where the total output of the blower 80 is divided into the primary, secondary and tertiary air streams. The primary air stream is removed from the air control mechanism by means of the primary air conduit 81 and caused to pass through a pulverizer 82, where a pulverized solid fuel is introduced to this primary air stream and then transported to the burner 83. At the same time, the secondary air, representing the main combustion air supply for the furnace is carried from the air control mechanism 1 to the burner by means of the secondary air duct 84. Tertiary air, whenever needed, is carried from the air control mechanism 1 to the burner 83 by means of the tertiary air duct 85. Although my invention is designed for use preferably with a solid fuel pulverizer especially designed for use with a pressurized sweeping fluid such as the one shown in my co-pending application, Serial No. 123,245 entitled Fluid Swept Ball Mill With Ball Moving Rotor and Stationary Drum, filed October 24, 1949, it may be conveniently used with any other type of solid fuel pulverizer. Where the pulverizer is of the type which absorbs a large amount of the kinetic energy of the primary air stream an induction fan may be placed in the primary air duct between the pulverizer 82 and the burner 83. My invention may be used with any one of a number of different types of burners. Preferably, it is designed for use With the burner described in my co-pending application entitled Improvement in Furnace Burners. My invention may be used in burners utilizing a liquid or gaseous fuel. The prime purpose of my unified air control, however, does not appear with these fuels because it is standard practice to burn both liquid and gaseous fuels with only a single air stream thereby eliminating the difiiculty of synchronizing the regulation of multiple air streams.

It will be seen that my unified air control provides a compact, precise and easily operable means for completely regulating all of the air introduced to the burner.

The foregoing description has been, in general, confined to the specific conditions of operation experienced when this draft control is employed with my improved burner and pulverizer, above identified. This is not to be interpreted as a limitation upon the flexibility and adaptability of my invention or upon its capacity to operate successfully with other types of systems involving very different operating principles. My draft control may be adapted to the needs of any unit system of pulverizing and burning.

Numerous modifications of my invention may be made each without departing from the principle thereof. Each of these modifications is to be considered as included in the hereinafter appended claims unless the language of these claims expressly states otherwise.

I claim:

1. In furnace firing equipment requiring a unified draft control structure for distributing proportioned amounts of primary, secondary and tertiary air, the combination including: a conduit from a common source of air under pressure; a chamber receiving said air; a main damper horizontally and adjustably slidable within said chamber; a plate having three rectangular apertures therein over which said main damper is horizontally movable; auxiliary dampers horizontally and adjustably movable in a direction transverse to the movement of said main damper to close individually said apertures in said plate; adjustable fillers upon the closing edges of said auxiliary dampers; internally threaded lugs depending from said auxiliary dampers; an externally threaded system of coaxial shaft and tubes engaging said threaded lugs so as to permit transverse movement of said auxiliary dampers individually from a single station; conduits beneath said apertures distributing the proportioned air streams.

2. In a furnace burner draft control, the combination comprising: a housing; baffics within said housing for dividing the interior thereof into a main chamber and a plurality of secondary chambers; a plurality of apertures in one of said baffles, each of said apertures communicating with said main chamber and with one of said secondary chambers; a damper in each of said secondary chambers at each of said apertures; means for individually reciprocating each of said dampers across its adjacent aperture; a main damper in said main chamber; means for moving said main damper across all of said apertures simultaneously; a port for admitting a fluid to said main chamber; a plurality of exhaust ports, one communicating with each of said secondary chambers, a filler plate mounted at the leading edge of each of said dampers associated with each of said apertures; said filler plates each being pivotable about its center to an aslant position with respect to the leading edge of the adjacent damper; means for detachably locking each of said filler plates to its supporting damper.

References Cited in the file of this patent UNITED STATES PATENTS 14,703 Risher Apr. 15, 1856 206,611 Rainey July 30, 1878 795,226 Jensen July 18, 1905 1,099,713 Morris June 3, 1914 1,263,074 Klutts Apr. 16, 1918 1,354,747 Hiller Oct. 5, 1920 1,683,372 Plantinga Sept. 4, 1928 1,914,828 I-Iardinge June 20, 1933 2,197,231 Walker Apr. 16, 1940 2,594,312 Kerr et al Apr. 29, 1952 

